MODES OF emergi:ng Fr.OM PUP^. 325 



eggs being laid on the outside of the grain, the 

 entrance of the caterpillar into the interior is not 

 larger than a pin's point, and of course entirely use- 

 less as a passage for the moth ; but, before its trans- 

 formation into the pupa, it shapes out a door in the 

 skin of the grain, so that it may be easily broken open 

 from within, while it appears entire on the outside. 

 By pushing it accordingly it at once gives way. 



A prospective contrivance of the same kind occurs 

 in the economy of a caterpillar which lives on the 

 dry pith in the seed heads of the wild teazle (Dipsa- 

 cus silvestris). The hole by which the newly hatched 

 caterpillar enters is so minute, that in some hun- 

 dreds of teazle heads, containing full-grown ones, 

 we have never been able to detect it ; but its subse- 

 quent proceedings are easily traced. From the first 

 it is not contented with the protection afforded by 

 the walls of the seed head, but always spins a gallery 

 of thick silk to cover it while feeding, the outside of 

 which is generally covered with its ejectamenta. Up 

 to the period of its approaching change, the walls of 

 the seed head are left quite entire, as it only eats the 

 dry pith contained in their cavity ; but through these 

 it would be impossible for the moth to make its way, 

 inasmuch as it is unprovided with mandibles for 

 gnawing. The provident caterpillar, therefore, takes 

 care before its change to cut a circular hole into the 

 teazle at the end of its own silken gallery, through 

 which the nascent moth may find an easy passage. 

 Bonnet gives it further credit for a piece of ingenuity 

 which we have not been able to verify. After cutting 

 the hole, he tells us, it carefully fortifies it on the out- 

 side by amassing the fibres and seeds of the plant in 

 a loose manner over the hole, to prevent the intrusion 

 of rapacious insects from without ; and he gives a 

 very minute detail of his discovery of this fortifica- 



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